1. Field of the Invention
The present invention relates to a failure diagnosis technique for a protecting tube type thermocouple.
2. Background Art
A thermocouple has been often used as a thermometer for industrial purpose. Various thermocouples are used according to a range of temperature to be measured, a state of a measured place, required accuracy, and the like.
The thermocouple is also used for temperature measurement for a heating furnace and the like. When the thermocouple is used for a long time in such a high-temperature atmosphere and temperature rise and fall are repeated, it is likely that the thermocouple itself is deteriorated.
Therefore, there is proposed a technique for easily detecting and predicting deterioration of the thermocouple. For example, there is a technique for supplying an electric current to the thermocouple, measuring temperature from a thermoelectromotive force generated by the thermocouple, comparing a resistance value corresponding to temperature calculated from a relation between temperature stored in advance and a resistance value of the thermocouple and a resistance value of the thermocouple measured from a voltage fall at the time when the electric current is supplied to the thermocouple, and detecting deterioration of the thermocouple (see Japanese Patent Application Laid-Open No. H8-313466). There is also a technique for providing a first thermocouple close to a measurement target and a second thermocouple that is in close contact with the first thermocouple and farther away from the measurement target than the first thermocouple, comparing an output of the first thermocouple and an output of the second thermocouple, and determining, when an output difference between both the thermocouples exceeds a predetermined value, that the first thermocouple is deteriorated (see Japanese Patent Application Laid-Open No. H9-218107).
In kneading of a material having high viscosity such as rubber or plastic, sensing of a kneading state is important. The temperature of a kneaded object is measured as an index indicating the kneading state (a kneading degree). For such measurement of the temperature of the kneaded object, a protecting tube type thermocouple (a thermocouple with protecting tube) is often used. The protecting tube type thermocouple is a thermometer in which a thermocouple element wire is protected from the atmosphere of a measurement target by, for example, a protecting tube made of metal.
Since the temperature of the kneaded object serves as the index indicating the kneading degree in this way, when wear, bend, breakage, or the like occurs in the protecting tube during the kneading, it is necessary to replace the protecting tube as soon as possible. A problem could also occur in that broken pieces due to breakage or the like are mixed in a kneading material and adversely affect a product.
To prevent such a problem from occurring, it is sufficient if it is possible to confirm that the protecting tube is not deteriorated. In other words, it is sufficient if it is possible to detect deterioration such as wear or fracture of the protecting tube as soon as possible and appropriately ascertain replacement timing for the protecting tube.